Minerals are natural occurring, inorganic materials of consistent chemical composition. Usually their atoms are arranged in a definite crystal structure. Most gemstones are minerals. Since they have a uniform chemical composition each mineral has consistent set of physical and optical properties.

Mineraloids

Material found in the earth that originated from living organisms such as amber and jet are called mineraloids.

Rocks

Rocks are a combination of two or more minerals. Gemstones such as lapis lazuli which is a mixture of lazurite, calcite and sometimes pyrite are classified as rocks.